Colloidal semiconductor nanocrystals are nanometer-sized fragments of the corresponding bulk crystals, which have generated fundamental interest for their promise in developing advanced optical materials. The size-dependent emission is probably the most attractive property of semiconductor nanocrystals, for example, differently sized CdSe nanocrystals can be prepared that emit from blue to red, with comparatively pure color emissions. These nanocrystal-based emitters can be used for many purposes, such as for light-emitting diodes, lasers, biomedical tags, and the like.
One type of useful nanocrystalline material is the core/shell nanocrystal, which features a nanocrystalline core of one type material, coated with a shell of another type material. Core/shell nanocrystals are representative of a number of different complex structured nanocrystals, such as core/shell/shell structured materials, the architectures of which are aimed at providing fine control over the nanocrystal's photophysical properties. However, synthetic methods for preparing high quality, nearly monodisperse core/shell and other complex structured nanocrystals have lagged behind those available for the synthesis of plain core nanocrystals.
What are needed are improved methods to produce high quality, highly monodisperse core/shell and other complex structured nanocrystals that provide materials that approach the same high quality as the plain core nanocrystals currently available. In particular, synthetic techniques are needed that allow the preparation of these complex structured nanocrystals to approach the same level of control over fundamental parameters such as, crystallinity, size and size distribution, as that attained in the synthesis of plain core nanocrystals. The availability of such synthetic methods should improve the quality of known core/shell structures, and should generate many unexplored nanostructures.